This invention relates to a control apparatus for a hybrid vehicle, and particularly to a control apparatus for a hybrid vehicle that controls charge and discharge performance of a main battery in a low temperature environment. The control apparatus extends the life of the main battery and improves the reliability of the entire control system.
Some motor vehicles are of a type commonly called a hybrid vehicle having an engine and an electric motor disposed therein as the power sources of a propulsion system. The engine mounted on the hybrid vehicle is provided to directly connect with an electrical motor having a vehicle driving function and an electrical power generating function. This hybrid vehicle has a control apparatus to control both driving and power-generating states of the electric motor based on a driving state of the hybrid vehicle and a driving state of the engine.
Control apparatus of a hybrid vehicle supplies drive electric power to an electric motor and establishes a main battery charged by generated electric power from the electric motor. When a quantity of charge of the main battery (defined xe2x80x9cSOCxe2x80x9d) becomes 0%, the control apparatus cannot drive the electric motor. When a quantity of charge of the main battery becomes 100%, the control apparatus cannot receive power-generation electricity from the electric motor. Accordingly, the control apparatus controls both driving and power-generating states so that a quantity of charge of the main battery is maintained in one limit or within a predetermined range.
In the main battery, there is a problem because the electric charge and discharge performances deteriorate when the main battery temperature goes low in a low temperature environment. The control apparatus needs to administer main battery temperature so that the electric charge and discharge performances do not deteriorate.
One such example of a control apparatus for a hybrid vehicle is disclosed in published Japanese Application Laid-Open No. 2000-92614 and published Japanese Application Laid-Open No. 2000-23307.
The control apparatus disclosed in published Japanese Application Laid-Open No. 2000-92614 controls a charge state of a battery to obtain in a predetermined temperature state. Specifically, when battery temperature is lower than the predetermined temperature, this control apparatus forcibly executes electric charge and discharge in the predetermined battery charge limits, and raises battery temperature by heat generated from this electric charge and discharge.
The control apparatus disclosed in published Japanese Application Laid-Open No. 2000-23307 starts up an engine by supplying electric power from a battery to a motor and executes driving of the motor by supplying electric power from the battery to the motor after engine start-up which causes battery temperature to rise. This occurs even after an engine is started for performing the power running operation of the motor when battery temperature is equal to or less than a predetermined value, when internal resistance of the battery is equal to or more than a predetermined value, when a charge state of the battery is equal to or more than a predetermined value, and when engine coolant temperature is equal to or less than a predetermined value as well.
However, the control apparatus indicated in the disclosure detects a charge state (SOC) of the main battery and administers electric charge and discharge of the main battery in either case, in order to avoid reduction of the electric charge and discharge of the main battery in a low temperature environment.
Accordingly, in the control apparatus indicated in the disclosure, in order to provide a means to detect a charge state (SOC) of the main battery, the system becomes complicated. There is a problem because of a rise in cost.
In order to obviate or minimize the above problem, the present invention provides a control apparatus for a hybrid vehicle having an engine and an electric motor disposed therein. The electric motor has both driving and power-generating functions to directly connect to the engine mounted on the hybrid vehicle. The hybrid vehicle includes a main battery which supplies driving electric power to the electric motor and is charged by generated electric power from the electric motor; a temperature sensor for detecting a temperature of the main battery; and a control means which controls to prohibit power-generation driving of the electric motor when a main battery temperature detected by the temperature sensor is under a set temperature, when the electric motor is power-generation driving, when an open-circuit voltage value of the main battery exceeds a set voltage value, and when a generated electric power value of the electric motor is under a set electric power.
A control apparatus of a hybrid vehicle of the invention controls to prohibit power-generation driving of the electric motor when a main battery temperature detected by the temperature sensor is under a set temperature, when the electric motor is used during power-generation driving, when an open-circuit voltage value of the main battery exceeds a set voltage value, and when a generated electric power value of the electric motor is under a set electric power. By this arrangement, the system does not need a means to detect a charge state of the main battery, can efficiently charge and discharge the main battery in the low temperature environment, and can well maintain a charge acceptance of the main battery.